Methods and apparatus for discrete mirror processing

ABSTRACT

A method is described for the processing of substrates for utilization as discrete mirrors. The method includes temporarily mounting a first end of at least one substrate onto a grinding machine plate, engaging a second end of the at least one substrate with a grinding wheel, rotating the plate and grinding wheel in opposite directions, and moving the grinding wheel and the plate toward one another at a rate.

BACKGROUND OF THE INVENTION

This invention relates generally to ring laser gyroscopes, and morespecifically, to methods and apparatus for processing of discretemirrors utilized in ring laser gyroscopes.

Discrete mirror processing for at least one known ring laser gyroscopeinvolves three processes normally used in optical fabrication,specifically, grinding, lapping, and polishing. The lapping andpolishing processes typically utilize a loose abrasive slurry. The looseabrasive slurry comprises multiple abrasive particles dispersed in aliquid medium, for example, water. Although loose abrasive slurries arewidely used in the lapping and polishing processes to provide anoptically clear surface finish on glass articles, loose abrasiveslurries also have many disadvantages associated therewith.

For example, such loose abrasive slurries must be periodically analyzedto assure quality and dispersion of the abrasive particles. Theequipment associated with the loose abrasive slurry process must also becontinually maintained. Maintenance of such equipment is costly due tothe labor costs associated with the maintenance. Further, additionalequipment is typically incorporated into the slurry process for thepreparation, handling and disposal of the loose abrasive slurrymixtures. Also, the cost of maintaining a loose abrasive slurry processis costly in term of raw materials, equipment maintenance, disposal ofused slurries and labor. Processes which use slurries are usually veryuntidy because the loose abrasive slurry splatters easily and isdifficult to contain.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a method for processing glass substrates for utilizationas discrete mirrors is provided. The method comprises temporarilymounting a first end of at least one substrate onto a grinding machineplate, engaging a second end of the at least one substrate with agrinding wheel, rotating the plate and grinding wheel in oppositedirections, and moving the grinding wheel and the plate toward oneanother at a rate.

In another aspect, a process for fabricating a mirror from a substrateis provided. The method comprises rotating an end of the substrate in afirst direction, configuring a grinding wheel with a matrix between nineand twenty-five microns, engaging the end of the substrate with thegrinding wheel, and rotating the grinding wheel in a direction oppositethat of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view illustration of a plurality of glass rods mountedto a grinding machine plate.

FIG. 2 is a side view of the plate and glass rods of FIG. 1.

FIG. 3 is a flowchart describing a glass rod grinding process.

DETAILED DESCRIPTION OF THE INVENTION

The methods and apparatus described herein provides for the eliminationof the loose abrasive slurry lapping process that is currently utilizedin the fabrication of high precision optics. Specifically, a grindingprocess that enables high precision optics to be ground to the same or abetter surface finish, with minimal sub-surface damage and clarity ascompared to conventional loose abrasive lapping is described. Thisgrinding process provides for the fabrication and modification of glassarticles such that the loose abrasive lapping process is eliminated andthe glass articles are moved directly to polishing processes.

FIGS. 1 and 2 illustrate a plurality of rods 10 mounted to a plate 12.In one embodiment, plate 12 is of the type that is utilized with agrinding machine. Utilizing the illustrated configuration provides forthe fabrication of discrete mirrors and substrates using a multi-speedgrinder (e.g., a grinding machine) enabling the elimination of looseabrasive slurry lapping. In an exemplary embodiment, plate 12 isattached to a NAG-250 multi-speed grinder on which is mounted a 9-25micron metal, metal/resin or resin bond matrix, for example, a ninemicron resin bond matrix diamond wheel. In the illustrated embodiment,plate 12 is a circular glass plate. Rods 10 include circular glass rodsranging from, for example, from 0.1 inches to about 3 inches, morespecifically, from 0.305 inches to about 2.50 inches in diameter. Glassrods 10 are evenly spaced and temporarily mounted on glass plate 12.While described in terms of glass rods, it is to be understood that theprocesses described herein are not limited to such rods. Rather,substrates including, but not limited to, wafers, rods, cubes or othergeometrical shapes may be polished as described herein.

In one embodiment, when attached to a grinding machine (not shown),glass plate 12 rotates clockwise at a speed of either about thirteen rpm(rough grind) or about four rpm (fine grind) while the grinding toolwithin the grinding machine rotates counter clockwise at a speed ofeither about 1000 rpm (rough grind) or about 1400 rpm (fine grind).

In addition to the rates of rotation, glass rods 10 (and plate 12) aremoved towards the grinding wheel at a rate. For example, a rough grindfeed rate is about 0.07 mm/min and a fine grind feed rate is about 0.015mm/min. In these embodiments, a 0.5% coolant and water mixture is usedto provide lubrication at the surfaces being ground and further helps toremove glass swarf between the surface of the grinding wheel and ends ofglass rods attached to plate 12.

FIG. 3 is a flowchart 100 illustrating a rod grinding process utilizingthe equipment and fixtures for grinding as described above.Specifically, glass rods 10 are mounted 102 onto a grinding machineplate 12. Rods 10 are mounted 102 at an end opposite the end that is tobe ground and polished. The ends to be polished are then engaged 104 bya grinding wheel of the grinding machine.

The grinding machine plate 12 and grinding wheel are rotated 106 inopposite directions, and the grinding machine plate 12 and grindingwheel are moved 108 toward one another at a specific rate.

After the above described grinding process, the surface finish on theglass rods is evaluated with a diamond stylus. One example of such adiamond stylus is commercially available under the trade designationMahr Pocket Surf available from Deterco, Inc., Houston, Tex. Initialsurface finishes or Ra values of the of the ground ends of glass rods 10typically fall within a range of 0.01 micrometer to 0.30 micrometer,while surface finishes utilizing a nine micron loose abrasive aluminumoxide slurry lapping process after an initial grinding range from 0.28micrometer to 0.30 micrometer. Sub-surface damage of the ground ends ofthe glass rods typically fall within 2.87 micrometers to 3.05micrometers while sub-surface damage of ground ends of glass rodspolished using the above described lapping process is between 3.10micrometers and 3.30 micrometers. The above described grinding processresults in substrates and/or glass rods having a surface compatible withpolishing processes that result in a polished substrate surface finishof between 1 Angstrom and 3 Angstroms.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for processing substrates for utilization as mirrors, saidmethod comprising: temporarily mounting a first end of at least onesubstrate onto a grinding machine plate; engaging a second end of the atleast one substrate with a grinding wheel; rotating the plate andgrinding wheel in opposite directions throughout processing to polishthe substrates; and moving the grinding wheel and the plate toward oneanother at a rate.
 2. A method according to claim 1 further comprisingproviding a liquid lubricant between the second end of the at least onesubstrate and the grinding wheel.
 3. A method according to claim 2wherein providing a liquid lubricant comprises using a 0.5% coolant andwater mixture to remove glass swarf between the grinding wheel and thesurface of the at least one substrate.
 4. A method according to claim 1wherein rotating the plate and grinding wheel comprises rotating theplate between about thirteen revolutions per minute and about fourrevolutions per minute.
 5. A method according to claim 1 whereinrotating the plate and grinding wheel comprises rotating the grindingwheel between about 1000 revolutions per minute and about 1400revolutions per minute.
 6. A method according to claim 1 wherein movingthe grinding wheel and the plate toward one another at a rate comprisessetting a feed rate between about 0.07 millimeters per minute and about0.015 millimeters per minute.
 7. A method according to claim 1 furthercomprising attaching a matrix to the grinding wheel, wherein attachingthe matrix comprises selecting at least one of a metal bond matrix and aresin bond matrix.
 8. A method according to claim 7 wherein selecting atleast one of a metal bond matrix and a resin bond matrix comprisesselecting a matrix having a particle size between nine and twenty-fivemicrons.
 9. A method according to claim 1 wherein the at least onesubstrate includes one or more of a wafer, a rod, and a cube fabricatedfrom glass.
 10. A method according to claim 1 wherein moving thegrinding wheel and the plate toward one another comprises moving thegrinding wheel and plate to provide a surface finish for the substrateof between 0.01 micrometer and 0.30 micrometer and sub-surface damagebetween 2.87 micrometers and 3.05 micrometers.
 11. A process forfabricating a mirror from a substrate comprising: rotating an end of thesubstrate in a first direction; configuring a grinding wheel with amatrix having a particle size between 9 and 25 microns; engaging the endof the substrate with a grinding wheel; and rotating the grinding wheelin a direction opposite that of the substrate throughout the fabricationof the mirror.
 12. A process according to claim 11 wherein rotating anend of the substrate in a first direction comprises rotating thesubstrate between about thirteen revolutions per minute and about fourrevolutions per minute.
 13. A process according to claim 11 whereinrotating the grinding wheel comprises rotating the grinding wheelbetween about 1000 revolutions per minute and about 1400 revolutions perminute.
 14. A process according to claim 11 further comprising providinga liquid lubricant at the engagement of the substrate and the grindingwheel.
 15. A method according to claim 14 wherein providing a liquidlubricant comprises using a 0.5% coolant and water mixture to removeglass swarf between the grinding wheel and the surface of the substrate.16. A method according to claim 11 further comprising moving thegrinding wheel and the plate toward one another at a feed rate betweenabout 0.07 millimeters per minute and about 0.015 millimeters perminute.
 17. A method according to claim 11 wherein the substrateincludes one or more of a wafer, a glass rod, and a cube.
 18. A methodaccording to claim 11 further comprising polishing to a resultantsurface finish of between 0.01 micrometer and 0.30 micrometer.
 19. Amethod according to claim 11 further comprising polishing to a resultantsub-surface damage of between 2.87 micrometers and 3.05 micrometers. 20.A method according to claim 11 further comprising polishing thesubstrate surface to a finish between 1 Angstrom and 3 Angstroms.